SDWebImage源码阅读(十一)SDWebImagePrefetcher

　　SDWebImagePrefetcherDelegate

 1 @protocol SDWebImagePrefetcherDelegate <NSObject>
 2
 3 @optional
 4
 5 /**
 6  * Called when an image was prefetched.
 7  *
 8  * @param imagePrefetcher The current image prefetcher
 9  * @param imageURL        The image url that was prefetched
10  * @param finishedCount   The total number of images that were prefetched (successful or not)
11  * @param totalCount      The total number of images that were to be prefetched
12  */
13 - (void)imagePrefetcher:(nonnull SDWebImagePrefetcher *)imagePrefetcher didPrefetchURL:(nullable NSURL *)imageURL finishedCount:(NSUInteger)finishedCount totalCount:(NSUInteger)totalCount;
14
15 /**
16  * Called when all images are prefetched.
17  * @param imagePrefetcher The current image prefetcher
18  * @param totalCount      The total number of images that were prefetched (whether successful or not)
19  * @param skippedCount    The total number of images that were skipped
20  */
21 - (void)imagePrefetcher:(nonnull SDWebImagePrefetcher *)imagePrefetcher didFinishWithTotalCount:(NSUInteger)totalCount skippedCount:(NSUInteger)skippedCount;
22
23 @end

　　代理提供了两个方法：

　　1.每次下载完成一个图片，finishedCount 表示对图像进行预取的总数（成功或失败）totalCount 图像将被预取的总数。

　　2.当所有的图像下载完毕，totalCount 对图像进行预取的总数（无论成功或者失败） skippedCount 跳过的图像的总数，表示下载失败的的总数。

　　命名block 

1 typedef void(^SDWebImagePrefetcherProgressBlock)(NSUInteger noOfFinishedUrls, NSUInteger noOfTotalUrls);
2 typedef void(^SDWebImagePrefetcherCompletionBlock)(NSUInteger noOfFinishedUrls, NSUInteger noOfSkippedUrls);

　　SDWebImagePrefetcher 属性

 1 /**
 2  *  The web image manager
 3  */
 4 @property (strong, nonatomic, readonly, nonnull) SDWebImageManager *manager;
 5
 6 /**
 7  * Maximum number of URLs to prefetch at the same time. Defaults to 3.
 8  */
 9 @property (nonatomic, assign) NSUInteger maxConcurrentDownloads;
10
11 /**
12  * SDWebImageOptions for prefetcher. Defaults to SDWebImageLowPriority.
13  */
14 @property (nonatomic, assign) SDWebImageOptions options;
15
16 /**
17  * Queue options for Prefetcher. Defaults to Main Queue.
18  */
19 @property (nonatomic, assign, nonnull) dispatch_queue_t prefetcherQueue;
20
21 @property (weak, nonatomic, nullable) id <SDWebImagePrefetcherDelegate> delegate;

　　SDWebImageManager *manager 网络图像管理器

参考链接:http://www.jianshu.com/p/9b629dbd4d30